John Gill Commentary 2 Kings 15:37

"In those days Jehovah began to send against Judah Rezin the king of Syria, and Pekah the son of Remaliah." — 2 Kings 15:37 (ASV)

In those days At the end of the days of Jotham, or after his death, things might be in design, and preparations made before, but nothing of what follows came to pass in his life, but in the times of his son;

the Lord began to send against Judah Rezin the king of Syria, and Pekah the son of Remaliah : to make war with them as a scourge to Ahaz for his sins; of which is in the following chapter.